This invention relates to a control method for valve-timing changeover for electronically controlled fuel injection type internal combustion engines that have selectable modes of valve-timing operation and is primarily applied to a vehicular engine.
There has been known heretofore from the Japanese Examined Patent Application Publication No. Tokkosho 49-33289 an engine in which a valve timing for at least each one of the intake valves or the exhaust valves can be changed over as desired between a low-speed valve timing suitable for a low-speed revolution range of the engine and a high-speed valve timing suitable for a high-speed revolution range of the engine. In this type of engine, the valve timing is changed over to the low-speed valve-timing in the region or range where revolution speed of the engine is lower than a predetermined speed and the intake negative pressure of the engine is also lower than a predetermined pressure level (closer to vacuum) while it is changed over to the high-speed valve-timing in conditions other than the foregoing region.
In an electronically controlled fuel injection type engine, an electronic control circuits including a micro-computer is used to calculate a fuel injection quantity by taking into account various parameters representing the operating condition of the engine. More specifically, when it is determined that a high load is being applied to the engine in view of such parameters as engine revolution speed, intake negative pressure, throttle opening, engine's water temperature, intake temperature, atmospheric pressure, etc. the fuel injection quantity is increased to enrich the air-fuel mixture. Under such a high-load operation of the engine, it is advantageous to the engine operation that the valve timing is changed over to the high-speed one. However, when the valve timing is changed over only on the basis of the revolution speed of the engine and the intake negative pressure as in case of the prior art, it is simply not possible to change over the valve timing to the high-speed valve timing to conform to a required fuel injection increase that is determined from a number of parameters as described above.
In view of the foregoing, it is the object of the present invention to provide a valve-timing changeover control method permitting the valve timing to be changed over to the high-speed valve timing at a proper time when the engine is operating under a high load necessitating an increase in the quantity of fuel injection.